**Unsteady Stagnation Point Flow of Hybrid Nanofluid Past a Convectively Heated Stretching**/**Shrinking Sheet with Velocity Slip**

### **Nurul Amira Zainal 1,2, Roslinda Nazar 1,\*, Kohilavani Naganthran 1 and Ioan Pop 3**


Received: 27 July 2020; Accepted: 22 September 2020; Published: 24 September 2020

**Abstract:** Unsteady stagnation point flow in hybrid nanofluid (Al2O3-Cu/H2O) past a convectively heated stretching/shrinking sheet is examined. Apart from the conventional surface of the no-slip condition, the velocity slip condition is considered in this study. By incorporating verified similarity transformations, the differential equations together with their partial derivatives are changed into ordinary differential equations. Throughout the MATLAB operating system, the simplified mathematical model is clarified by employing the bvp4c procedure. The above-proposed approach is capable of producing non-uniqueness solutions when adequate initial assumptions are provided. The findings revealed that the skin friction coefficient intensifies in conjunction with the local Nusselt number by adding up the nanoparticles volume fraction. The occurrence of velocity slip at the boundary reduces the coefficient of skin friction; however, an upward trend is exemplified in the rate of heat transfer. The results also signified that, unlike the parameter of velocity slip, the increment in the unsteady parameter conclusively increases the coefficient of skin friction, and an upsurge attribution in the heat transfer rate is observed resulting from the increment of Biot number. The findings are evidenced to have dual solutions, which inevitably contribute to stability analysis, hence validating the feasibility of the first solution.

**Keywords:** hybrid nanofluid; unsteady stagnation point; velocity slip; convective boundary condition; stability analysis
